The present invention relates to the steaming of tubular knitted fabrics in finishing operations and particularly to an improved apparatus for the application of dry steam to both sides of the fabric simultaneously.
In the processing of tubular knitted fabric it is conventional practice to direct the tubular fabric over an internal spreading device, often referred to as a spreader or propeller. The device distends the fabric laterally to a predetermined uniform width, typically advancing the fabric by means of longitudinally moving belts engaging the inner edge walls of the fabric. While the fabric is held in its laterally distended condition, and while it is being advanced through the finishing equipment, it is subjected to a steaming operation, to relax the fibers and enable the fabric to readjust to its laterally distended, geometrically uniform condition. To a large extend, the fabric then tends to retain this geometric condition when it is delivered at the discharge end of the spreading device.
Typically, the distended fabric is conveyed and steamed while the fabric occupies a horizontal plane. Consequently, it is necessary to avoid condensation on the portions of the finishing equipment located directly above the fabric being processed. Otherwise, the condensed water would eventually drip down upon the face of the fabric causing water spots and thereby greatly detract from the value of the processed fabric.
In accordance with well known principles, the condensation problem is substantially eliminated by providing a steam discharge means comprising a steam pipe enclosed by a steam discharge housing. The pipe includes longitudinally spaced perforations to permit the escape of steam into the confines of the housing. The housing generally comprises an inner channel member having legs and an outer channel member having legs partially enclosing the inner channel member. The legs of the inner channel member have inturned ends forming baffles and the legs of the outer channel member have inturned ends in a parallel, spaced relation to the legs of the inner channel member forming therewith slots for the escape of steam. Means are provided for withdrawing condensation from within the housing. The above-described arrangement is extremely effective in removing condensation caused by the partial cooling of the steam as it expands upon discharge from the steam pipe. Moreover, the pressure of the steam within the outer channel member is higher than the steam passing through the slots, thereby maintaining the slots at a sufficiently high temperature to prevent the formation of droplets of water in the slots. Consequently, only dry steam will be discharged to the upper surface of the fabric being processed and the fabric will be steam treated without the danger of water-spotting.
It is an important goal of the tubular knit fabric manufacturing industry to increase the overall rate of production for the fabric. Yet, the speed of a typical finishing process is generally limited by the ability to effectively impart steam to the fabric. Merely increasing the rate of steam application, using conventional equipment, has been found to be ineffective inasmuch as greater volumes of steam give rise to unwanted condensation problems notwithstanding the utilization of the above-described dripless steam discharge arrangement. This is due to the fact that the higher rates of steam flow cause condensation problems after the steam is issued from the steam boxes.
An advantageous process for steaming the fabric while increasing the rate of production is disclosed in the Frezza U.S. Pat. No. 3,868,215. In accordance with the teachings of the Frezza patent, the discharged steam is generally confined around the path of conveyance for the fabric. The confinement of the steam in contact with the fabric immediately following its issuance from the steam box, greatly enhances the ability of the steam to achieve the desired levels of penetration of the fabric within a short period of time. As a result, it is possible to significantly increase the speed of passage of the fabric.
A primary objective of the present invention is to further improve the overall rate of production for the fabric by providing a novel and improved apparatus for discharging steam in a dry condition and confining it to the immediate vicinity of the path of conveyance for the fabric and further providing means to prevent condensation of the discharged steam within the confining structure. Generally, a pair of steam boxes of the above-described type are mounted in an opposed relation on opposite sides of the plane occupied by the fabric to be processed. In accordance with a significant aspect of the invention, a wall-forming member is mounted on the discharge side of each of the steam boxes and extends in both the downstream and upstream directions of the path of fabric conveyance. Moreover, the opposed steam boxes are provided with end plates arranged in a close-fitting relation to one another along the sides of the conveyance path. Significantly, the contacting end plates and wall-forming members define a steam confining chamber closely surrounding the spreader and fabric. The chamber is arranged to form a zone not substantially greater in height at any given point than the distance from the steam discharge ducts to the fabric surface. Accordingly, a highly effective steam penetration is achieved in a relatively short time period.
The improved arrangement for the steam box provides, in an efficient, straightforward manner, a construction to achieve the desired steam confining capabilities with a structure that lends itself to easy and inexpensive manufacture. Moreover, the disclosed steam box is of compact design and therefore occupies a minimum of space to permit the most effective utilization of a factory production area.
In accordance with another important feature of the present invention, the wall-forming member of the upper steam box includes means for heating the surface thereof. In a preferred form, the heating means comprises a plate which is co-extensive with the wall-forming member and securely mounted thereon. The plate is provided with a passage-forming means whereby high pressure steam may be circulated across the surface area of the plate to maintain the upper regions of the steam confining chamber at a sufficiently high temperature to prevent the formation of droplets of condensed water.
To accommodate the passing through of the fabric being processed, the steam apparatus of the invention includes a series of hinged, relatively narrow flap elements at the entry and exit openings of the steam confining chamber. The hinged flap elements are mounted on the front and rear edges of the wall-forming member of the upper steam discharge box. Magnetic elements are carried by the flap elements or by a wall-forming member of the lower steam box whereby the hinged elements normally will be held in a closed condition by magnetic attraction. The machine operator opens a sufficient member of the hinged elements to accommodate the width of the particular fabric being conveyed through the steaming apparatus. The remaining hinged elements are kept closed to act as confining elements for the steam chamber. The magnetic attraction of the flaps is sufficiently strong to prevent steam pressure, within the steam confining chamber, from opening the hinged elements.
The disclosed steaming apparatus provides a highly effective means for discharging dry steam toward both surfaces of a fabric and for effectively confining the steam in the vicinity of the fabric to greatly increase the rate of production for the processing of the fabrics. The wall-forming members define a processing chamber of minimum volume, sufficient to enclose the fabric and spreader while minimizing the volume of confined steam. Moreover, by heating the upper wall-forming member of the chamber any problem with diverted steam, condensation of steam over the fabric is avoided.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description and the accompanying drawings.